A usual design of a side airbag module includes a gas generator mounted inside a cavity in a seat back rest, under a fabric cover near a vehicle roof above a door, or in a side panel in the body of a vehicle door. Side airbags mounted in a door or in a vehicle seat are usually designed to make contact with the lower torso of a seat occupant. Side airbags mounted in the roof area typically drop down to form an inflated side curtain to primarily protect the head and upper torso of the seat occupant. It is also possible to mount a side curtain airbag along a lower edge of a window with the airbag inflating upward to form the side curtain. In the event of a lateral impact on the vehicle or of an imminent lateral impact, the gas generator projects inflation gas into an airbag cushion, thereby inflating the airbag cushion. The airbag cushion of an airbag forming a side curtain typically expands into a space between a vehicle occupant and the vehicle window, thereby protecting the occupant from injuries that may be caused by a hard contact with the vehicle window, by broken glass, or by objects penetrating the window. Side impact airbags mounted in the door below the window are typically covered by a door trim panel that has been provided with tear lines and a live hinge. When the airbag inflates, the tear line tears open, and the panel hinges out of the way of the inflating airbag.
The gas generator is typically a pyrotechnical device triggered by an electronic signal from a side impact sensor. Accordingly, the proper function of a side impact airbag depends on the availability of electrical power and an electronic controller. Low-cost vehicles usually do not have a profit margin wide enough to allow for complex electronics. Furthermore, even if a vehicle has an electronic system for triggering the airbag, a conventional side impact airbag depends on proper functioning of the electronic system and the electric power supply.